Fire resistant organosiloxane elastomer foams and method of preparing same



Un ted States Patent ce j f3;,

Ronald L. Joyce, Midland, Mich., assignor to Dow Cor- I ning Corporation, Midland, Mich., a corporation of Michigan No Drawing. Filed June 2, 1958, Ser. No. 738,948

8 Claims. (Cl. 260-25) This application relates to organosiloxane elastomer foams of reduced flammability.

' Organosiloxane elastomer. foams are disclosed and claimed in United States application Serial No. 708,369, filed January 13, 1958, now abandoned, and assigned to Dow Corning Corporation. These foams are prepared by mixing (1) 100 parts by weight of a hydroxylated organopolysiloxane having a viscosity of at least 50 cs. at 25 C. and having an average of 1.9 to 2.0 monovalent hydrocarbon radicals, halogenated monovalent hydrocarbon radicals or hydrogen atoms per silicon atom, there being at least one hydrogen bonded to silicon in from 1 to 75% by weight of the siloxane units present and the the ratio of organic substituents to silicon atoms being at least 1.25/1, (2) 0 to 50 parts of a hydroxylated compound and (3) .1 to by weight of tin added as a stannous salt of a carboxylic acid. The mixed ing'r'ed-ients are allowed to stand at room temperature and a cured elastic foam is obtained.

The elastic foams prepared as above are thermally stable, suitable for thermal insulation, for cushioning against mechanical shock and for damping. However, because of the cellular form of the foamga large surface area is presented and thecured silicone rubber foam is flammable. It is quite apparent that a flammable foam is undesirable for many applications. Therefore, applicant sought additives which would act as fire retardants for such foams.

The primary object of thisinvention is to produce fire resistant silicone rubber foam at room temperature. -Another object is to find additives for known room-temperature curing silicone rubber foam systems to render the ultimate product fire retardant. Further objects 'and advantages of this invention are apparent or are specifi cally disclosed in the specification and claims which follow.

Applicant has found that the addition of 5 parts or more by weight [of nickelous bromide, aromatic pentabromoethyl benzene or aromatic pentabromo toluene to 100 parts by weight of the foam forming composition-outlined above, imparts fire retardant properties to the foam.

In the foams employed herein the siloxane (1) can be either a copolymer in whichthe SiH and SiOH appear in the same molecules or it can be a'mixture of a, hydroxylated siloxane (a) and a SiH-containing Siloxane (b). Regardless of whether (1) is a copolymer of hydroxylated siloxanes and SiH-containing siloxanes or a mixture of these two types of materials, the overall com? position of (1) must be within the above-defined range.

If the amount of siloxane units having SiH linkages is less than 1% by weight of (1), insufficient foaming is obtained. If the amount of SiH is above 75% by weight,

inferior elastomers are obtained. Preferably the amount age from 1.9 to 2 monovalent hydrocarbon or halogen- 2 ated'monovalent hydrocarbon groups per silicon atom and has a minimum viscosity of 50 cs. ;There is no'critical upper limitto the viscosity of (a) so that itlcan range in viscosity from relatively thin fluids to non-flowing g'ums.- (a) can be either homopolymeric or copoly'merici Siloxane component (b) must be present in the 'mixtui'e in amount so that the total weight percent of siloxane units having at least one H bonded to the silicon is from 1- to %;by weightof the total weight of mixture (1); The viscosity of b) is not critical and may range from materials of 1 to 2 cs. up to nonflowing gums. When (b) is a gum it is desirable to employ a solvent'suchas benzene, etherorthe like in order to insure thorough mixing.- e e --'f Siloxane (b) can be a completely condensedmaterial such as cyclic si-loxanes or triorganosilyl end-blocked siloxan'es or it may=also contain SiOH groups. (b) can be homopolymeric or copolymeric,'and those valences of. the silicon which arenot satisfied by H and O atoms are satis fied by monovalent hydrocarbon or halogenated monova lent hydrocarbon radicals. Preferably there is on the average of at least 1 monovalent hydrocarbon or halo* genat ed monovalent hydrocarbon radical per silicon'atom.

Specific examples of copolymeric siloxanes which can be employed as siloxane (1) are'10 mol percent ethyhy drog'ensiloxane and mol percent ethylmethylsiloxane; 25 mol percent HSiO 25 mol percent dimethylsiloxane and 50 mol percent phenylmethylsiloxane; and 1 mol percent r'nonophenylsiloxane, 5 mol percent H SiO, 4 mol percent octadecylmethylsiloxane and 90 mol percent di-. methylsiloxane. All of these copolymers contain SiOI-I groups.

Specific examples of mixtures which can'be employed assiloxane 1) are mixtures of a hydroxylated dimethyl- 'siloxane and (CH HSiO) ,"m'ix-tures of a hydroxylated copolymer of dimethylsiloxane and diph'enylsiloxane and a copolymer of methylhydrogensiloxaneand trime thylsiloxane'and mixturesi-of afhydroxylated copolymer of monomethylsiloxa'ne and dimethylsiloxane and 9. cm polymer of methylhydrogensiloxane and dimethylhydrogensiloxane. i i

Siloxane (1) both mixtures andcopolymers, can con tain any of the following types of siloxane units, RSiOm, R SiO, R SiO RHSiO, HSiO RH' SiO, H Si'O and SiO These variou units must be in the proportions such that the ratio of organic radicals and hydrogen atoms to silicon will fall w'ithinthe' above. defined limits.

For the purpose of this invention the R groups onthe silicon can be any monovalent hydrocarbon radical such as alkyl radicals such as methyl, ethyl, propyl or octadecyl; allkenyl radicals such as vinyl, allyl and hexenyl'g cycloaliphatic radicals such as cyclohexyl, cyclopentyl and cyclohexenyl; aralkyl hydrocarbon radicals such as beniyl and aryl hydrocarbon radicals such as phenyl, tolyl, naphthyl and xenyl. The R groups canalso be any halogenated monovalent hydrocarbon radical such as chloro phenyl, trifluorovinyl, chlorodifluorovinyl, tiifluoropropyl,

droxylated compound 2) is'present in amount f rom "1 l to 50% by'weight'based'on the weight of siloxanei(1);

The function of this hydroxylated compoundis to furnish excess hydroxyl groups for reaction with the silane hydrogen in order to produce sufficient gas to foam the composition. If desired, a mixture of two -or more hydroxylated'compounds (2) can be employed.

For purpose of this invention any hydroxylated compound either organic-or-inorganicwhich is at least partially compatible with the siloxane system is operative. Thus hydroxylated compound (2) can be, for example, hydroxylated organosilicon compounds-such as silanols, e.g. trimethylsilanol, triphenylsilanol, triethylsilanol and dirnethylsilanediol and low molecularweight hydroxylated siloxanes such as sym-tetramethyldisiloxanediol; :water; carboxylic acids-such as;formic, acetic, isobutyric, ma- Ionic, caproic, succinic, -benzoic, pchloroacrylic, acetoacetic, chloroacetic, acetonedicarboxylic, mercaptoacetic, bromomalonic, ot-cyanopropionic, succinamic and a-hydroxy-o-toluic acids and Belanine;and-alcoholsof less than twelvecarbon atoms. These alcohols can be monohydric monofunctional alcohols such as ethanol, isopropanol, butanol, tertiary-butanol and cyclopentanol; monohydric polyfunctional alcohols such as 2,2'-thio'diethanol, Z-aminoethanol, acetol, acetoin, 2,2,2-trichlorol-ethoxyethanol, furfuryl alcohol, glycol monoacetate, ozhydroxyisobutyronitrile, lactic acid, cyanic acid, 4-hydroxy-4-methyl-2-pentanone, 2-propyn-1-ol, isothionic acid, aodol, gamma-chloroallyl alcohol,,2-nitro-1-butanol, Z-fiuoroethanol, glycidol and hydracrylonitrile; polyhydric alcohols containing no ,other function suchas ethylene glycol, propylene glycol, 1,6-hexanediol, glycerine, pentaerythritol and glucose and polyhydric polyfunctional alcohols such as triethanolamine, diethylene glycol, pentaethylene glycol, 3-butene-1,2-diol, bromalhydrate, l-thioglycerol, glycerol fl-mononitrate, glycerol ether, allanturic acid, arabonic acid and 2-ethyl-2-nitro- 1,3 -propanediol.

It should be understood that the use of hydroxylated compound (2) is optional-since foams can be obtained by merely employing a mixtureof siloxane (1) and the catalyst. This is particularly true where siloxane (1) contains a relatively low viscosity hydroxylated fluid. "However, it is preferred to employ at least 1% of hydroxylated compound (2) since this gives superior foams. Mutual solvents such as dioxane, ethers, benzene or the like may be used to disperse (2) in 1).

The catalysts which are essential in the method of this invention are stannous salts of carboxylic, acids. These should be employed in amounts such that there is from .1 to 10.%by weight tin based on the weight ofsiloxane (1). For the purpose of this invention the stannous salt of any carboxylic acid is operative. Thisdincludes, for example stannous salts such as stannous acetate, stannous oleate, stannous stearate, stannous linoleate,.stannous naphthenates, stannousbenzoate, stannous naphthoate, stannous succinate, stannous sebaeate, stannous lactate, stannous maleate, stannous crotonate, stannous salicylate, stannous phthalate, stannous mandelate,.stannous cinnamatc and the stannous salt of phenyl acetic acid.

The fire retardant additives employed are nickelous bromide, aromatic pentabromo ethyl benzene and aromatic pentabromo toluene. These materials and methods of making them are known. They are added-in amounts of at least 5 parts by weight per 100 parts of (1), (2) and (3). The upper limit on the amount of fire retardant additive employed is a practical rather than an operational limit. Thus, whereas 30 or even 50 parts of additive can be used, little is gained by using more than 25 parts per 100 parts of foam composition.

In carrying out the process of this invention the various ingredients can be mixed in any desired fashion. Thus, for example, one may mix all the ingredients simultaneously or one may mix a hydroxylated'siloxane and a hydrogen containing siloxane to make up ingredient (1;) and then dissolve the catalysts in; hydroxylated-compound canized and cured at room temperature.

( 2) and thereafter mix the two mixtures and add the fire retardant additive. In fact, it is often desirable to mix the catalyst and hydroxylated compound (2) particularly in those cases where the catalyst is not particularly soluble in siloxane (1). Thus an alcohol soluble salt can be incorporatedin the mixture quite readily by firstdissolving it in an alcohol whichserves as hydroxylated compound (2).

After the catalyst and siloxane (1) have been brought together foaming of the compositions of this invention begins in avery short time and is generally complete within 5 to 20 minutes. At the end of. this time the siloxane elastomer has gelled so that a permanent elastomeric foam is obtained.

The density of the foams prepared by the method of this invention can vary from .5 pound per cubic foot upwards. In general the less dense foams are obtained under conditions which give the more rapidevolution-of hydrogen coupled with conditions where gelation of the elastomerdoes not take place until a considerable degree of expansion has been obtained. Thus for the less dense foams it is desirable to .use larger amounts of the SiH compound and/or larger amounts of the hydroxylated compound (2) than one would employ for the more dense foams. Also foams of lighter density can be obtained by. gentle warming of the mixture during foaming. In fact it is'often desirable but not essential that the mixtures be warmed during foaming particularly where ,extremely light and soft sponges are desired.

If desired, fillers can be incorporated in the elastomeric foams-of this invention. Any desired filler can be employed although the preferred fillers are inorganic materials such as metal oxides such as titania, zinc oxide, ferric oxide and magnesium oxide; siliceous materials such as clay, diatomaceous earth, fume silicas, silica aerogels, and silica xerogels; ceramic materials such as powdered glass; asbestos; powdered metals such as powdered aluminum and silicon and carbon black. The, fillers can be employed in any desired amount.

If desired, the compositions of this invention can contain other additives normally employed in silicone rubbers'such as oxidation inhibitors, compression ,set additives, pigments and the like.

The compositions of this invention are particularly useful in thermal insulation where extremes of temperaturetareto be encountered. For example, they can be applied to incompletely fabricated articles which must subsequently be heated during the fabrication process. Thus, forexample, the composition could be sprayed on the inside of an automobile body prior to application of the external enameled finish. The body can be subsequently enameled and then put through the enamel baking process without deteriorating the insulating foam on the inside of thebody.

The following examples are illustrative only and should notbe construed as limiting the invention which is properly delineated in the appended claims.

Example 1 parts by weight of a hydroxylated dimethyl polysiloxanefiuid having a viscosity of about 4750 cs. at 25 C.,'8 parts of-a linear siloxane of the formula (CH Si0[ (CH SiO],,Si(CH having a viscosity of 20 cs. at.25 C., 5 parts (C H CH SiOH andy25 parts of-diatomaceous earth were admixed and 10 parts by weight of anhydrous nickelous bromide was added and dispersed in the mixture. 5 parts by weight of stannous octoate was added to the mixture and a panel of foam 0.5- inch thickwas formed. The panel was vul- After five days, the panelwassplit and one ,sectionwas further curedat 250" C. for 24 hours. Specimens were cut from the panels.

" The above procedure was repeated employing 10 parts by weight of pentabromo ethyl benzene and again with 10 parts by weight pentabromo toluene in place of the nickelous bromide. A control was also prepared with- .out any fire retardant additive. The last samples measmed .5 by .5 by inches. Each sample had a natural foam skin on two opposite faces, open cells on the other two faces and on the end surfaces. Each sample was marked with lines spaced 1 inch from each end. Thus, from either end there was one line 1 inch from the end and another line 4 inches from the end. One end of .each's'ample was placed in a clamp ona ring stand. The longitudinal axis of the sample was horizontal and the transverse axis was at 45 to the horizontal. A wire gauze was clamped in a horizontal position .5 inch below the sample with about .5 inch of the sample extending beyond the edge of. the gauze. A standard inch Bunsen burner was adjusted with air ports open to producea blue flame about 1 inch high. The tip of the flame was brought into contact with the end of the sample while the Bunsen burner was inclined at 45 from the horizontal. The flame was held in contact with the end of the sample for 5 seconds and was then assua e That which is claimed is: 1

1. A method of preparing a fire resistant siloxane elastomeric foam which comprises mixing ('1) an'organopolysiloxane containing silicon-bonded OH groups having a viscosity of at least 50 cs. at 25 C. and. having per silicon atom on the average from 1.9 to, 2 radicals of the group consisting of monovalent hydrocarbon radicals, halogenated monovalent hydrocarbon radicals and hydrogen atoms, in said siloxane there being from 1 to 75% by weight siloxane units containing at least one'siliconbonded hydrogen atom and said siloxane containing an average of at least 1.25 of .total monovalent and' halogenated monovalent hydrocarbon radicals per silicon atom, (2) up to 50% by weight'based on the weight of siloxane (1) of a hydroxylated compound selectedfrom the group consisting of silanols, low molecular weight .hydroxylated siloxanes, water, carboxylic acids and alcoedge of the test specimen-after reaching the 1 inch mark v was recorded as the flame propagation. The time for hols of less than twelve carbon atoms,"(3) stannous salt of a carboxylic acid in amount suflicient to give from .1

to 10% by weight tin based on the weightof siloxane- .(1) and (4) at least 5% by weight of (1), (2)and (3) of a compound selected from the group consisting I'of nickelous bromide, aromatic pentabromoethyl benzene and ammatic pentabromo toluene, and thereafterallowing the mixture to'foam.

-phenyl radicals'and wherein-the catalyst (3) is a stannous salt of an aliphatic carboxylic acid.

4. A fire resistant elastomeric siloxane rubber foam comprising the reaction product of (1) an organopolysiloxane containing silicon-bonded OH groups and having a viscosity of at least cs. at 25 C. and having per silicon atom an average of from 1.9 to 2 radicals selected from the group consisting of monovalent hydrocarbon radicals, halogenated monovalent hydrocarbon radicals and hydrogen atoms, in said siloxane there being from 1 Room Temperature Cure Cure at 250 0.]24 hours First Ignition Second Ignition First Ignition Second Ignition A B C A B O D E F D E F Qontrol Totally 33 2. 75 Totally 1. 17 3.67

burned. burned Nickelous Bromide- 0 42 0 0. 17 0 0. 33 0 08 Aromatic Pentabromo Ethyl Benzene 0 0 0 08 0.5 1.0 0 0.67 Aromatic Pentabromo Toluene 0 0. 08 0 08 0.5 1.17

A, A, D, D-Propagation in inches. B, B, E, E'Propagation time in minutes. 0, O, F,

Example 2 Equivalent results were obtained from the method and procedure of Example 1 employing 4 parts by weight N-propyl orthosilicate, 100 parts by weight hydroxylated dimethylsiloxane polymer, 10 parts by weight hydroxyl end-blocked dimethylsiloxane polymer, 10 parts methyldiphenyl-silanol, 10 parts by weight trimethylsilyl end- .blocked methylhydrogensiloxane, 25 parts diatomaceons .earth and 7 parts of nickelous bromide, pentabromo- .ethylbenzene or pentabromo toluene.

The use of -a wide variety of formulations for the foams is contemplated. The addition of the fire-retardants of this invention to any of the foams specifically disclosed in the US. patent application Serial No. 708,369, filed January 13, 1958, now abandoned, will produce a fire resistant foamed silicon rubber. Other variations in the foam are obvious to those skilled in the art and are iincluded herein.

F-'.lime in minutes for extinguishing or for total burning.

to 75 by weight siloxane units containing at least one silicon-bonded hydrogen atom and in said siloxane there being on the average at least 1.25 of total monovalent and halogenated monovalent hydrocarbon radicals per bromide, aromatic pentabromo ethyl benzene and ar o' matic pentabromo toluene.

5. method of preparing a fire resistant siloxane elastomeric foam which comprises mixing (1) a mixture of (a) an organopolysiloxane containing silicon-bonded OH groups and having a viscosityof at least 50 cs. at 25 C. and having anaverageof from 1.916 [organic radicals of thej'group consisting of monovalenthydrocarbon 'r'adical's and halogenated l nionovalenthydrocarbon radicals per silicon atom and (b) a siloxane .containing siliconbonded hydrogen. inarnount such that there' is from 1 to 75% byfw vei ghtlba sed' on. the weight of (a) of 's'iloxane units containing atleast one silicon-bonded hydrogen atom the remaininggroups attached to the silicon in (b) the group consisting of nickelous bromide, aromatic pentabromo ethyl benzene and aromatic pentabromo Itoluene, andthereafter allowing the mixture to foam. 6. The method in accordance with claim in which all of the organic radicals in siloxane mixture (1) are methyl radicals and wherein the catalyst (3) is a stannous salt of an aliphatic carboxylic acid.

7. The rnethod in accordance with claim 5 wherein all of the organic radicals in siloxane mixture (1) are methyl and phenyl radicals and wherein the catalyst (3) is a stannous salt of an aliphatic carboxylic acid.

8. A fire resistant elastomeric siloxane rubber foam comprising thereaction prodpct of (1,) amixture of. (a)

an organopolysiloxane containing silicon-bonded OH groups and having a visco sity of at least 50 cst at C. and having an average of .from 1.9 to 2 organic radicals fofthe group consisting, of i onogalent hydrocarbon radicals and halogenatedrnonovalent hydrocarb n radtcals per silicon atom and (b) a siloxane containi ng silic on- -bondedhydrogen atoms in amount suchthat there, is from 1. to 75% .by, weight siloxane units containing at le ast one silicon-bonded hydrogen atom based on the weight of (a), the remaining. groups attached tothe silicpnin (b being organicradicalsselected from the groupconsis ting of monovalent hydrocarbon radicals and halogenated monovalenthydrocarbon radicals, (2) from 1 to 50% by weightbased onthe weight of (1.) of ahydroxylated compound selected from the group consisting of sil anol s, low. molecular weight hydroxylated siloxanes, water, car- 'boxylic acids and alcohols of less thantwelve carbon atoms, (3) a stannous salt of a carboxylic acid in amount suflicient to give from .1 to 10% by weight tin based on (1), and (4) at least 5% by weight of (l), (2) and (3 .of a compound selected from the group consisting of nickelous bromide, aromatic ,pentabromo ethyl benzene .and aromatic pentabrorno toluene and thereafter allowing the mixture to foam.

7 ReferencesCited in the file of this patent UNITEDSTATES PATENTS 2,676,927 McCurdy et al. Apr. 27, 1954 FOREIGN PATENTS 784,826 Great Britain Oct. 16, 1957 

1. A METHOD OF PREPARING A FIRE RESISTANT SILOXANE ELAS TOMERIC FOAM WHICH COMPRISES MIXING (1) AN ORGANOPOLYSILOXANE CONTAINING SILICON-BONDED OH GROUPS AND HAVING A VISCOSITY OF AT LEAST 50 CS. AT 25*C. AND HAVING PER SILICON ATOM ON THE AVERAGE FROM 1.9 TO 2 RADICALS OF THE GROUP CONSISTING OF MONOVALENT HYDROCARBON RADICALS, HALOGENATED MONOVALENT HYDROCARBON RADICALS AND HYDROGEN ATOMS, IN SAID SILOXANE THERE BEING FROM 1 TO 75% BY WEIGHT SILOXANE UNITS CONTAINING AT LEAST ONE SILICONBONDED HYDROGEN ATOM AND SAID SILOXANE CONTAINING ON AVERAGE OF AT LEAST 1.25 OF TOTAL MONOVALENT AND HALOGENATED MONOVALENT HYDROCARBON RADICALS PER SILICON ATOM, (2) UP TO 50% BY WEIGHT BASED ON THE WEIGHT OF SILOXANE (1) OF A HYDROXYLATED COMPOUND SELECTED FROM THE GROUP CONSISTING OF SILANOLS, LOW MOLECULAR WEIGHT HYDROXYLATED SILOXANES, WATER, CARBOXYLIC ACIDS AND ALCOHOLS OF LESS THAN TWELVE CARBON ATOMS, (3) STANNOUS SALT OF A CARBOXYLIC ACID IN AMOUNT SUFFICIENT TO GIVE FROM .1 TO 10% BY WEIGHT TIN BASED ON THE WEIGHT OF (1), (2) AND (3) (1) AND (4) AT LEAST 5% BY WEIGHT OF (1), (2) AND (3) OF A COMPOUND SELECTED FROM THE GROUP CONSISTING OF NICKELOUS BROMIDE, AROMATIC PENTABROMO ETHYL BENZENE AND AROMATIC PENTABROMO TOLUENE, AND THEREAFTER ALLOWING THE MIXTURE TO FOAM. 